The present invention relates generally to intervertebral defect devices, and more particularly, to an intervertebral defect device for insertion into an intervertebral space using minimally invasive techniques.
Referring to prior art FIGS. 9 and 10, the spine 120, also known as the vertebral column or the spinal column, is a flexible column of vertebrae 100 (special types of bones) held together by muscles, ligaments and tendons. The spine 120 extends from the cranium (not shown) to the coccyx 126, encasing a spinal cord 128 and forming the supporting axis of the body (not shown). The spinal cord 128 is a thick bundle of nerve tissue (nerves) that branch off to various areas of the body for the purposes of motor control, sensation, and the like. The spine 120 includes seven cervical vertebrae (not shown), twelve thoracic vertebrae (not shown), five lumbar vertebrae, LI–LV, five sacral vertebrae, SI–SV, and three coccyx vertebrae 126. The sacral and coccyx vertebrae are each fused, thereby functioning as a single unit. FIG. 10 shows the lumbar region 122, the sacral region 124 and the coccyx 126 of the spine 120 and that the vertebrae 100 are stacked one upon another. The top portion 100a and bottom portion 100b of each vertebrae 100 is slightly concave. The opposing concave vertebral surfaces form the intervertebral space 121 in which an intervertebral disk (not shown) resides. Each of the intervertebral disks has a soft core referred to as a nucleus pulposus or nucleus (not shown).
In FIG. 9, directional arrow 101a is pointing in the posterior direction and directional arrow 101b is pointing in the anterior direction. FIG. 9 shows that each vertebrae 100 includes a body 106 in the innermost portion, a spinal canal 108 and a spinous process 102 at the posterior-most end of the vertebra 100. The vertebrae 100 are substantially similar in composition, but vary in size from the larger lumbar vertebrae to the smallest coccyx vertebrae 126. Each vertebrae 100 further includes two transverse processes 104 located on either side and a protective plate-like structure referred to as a lamina 110. Nerves from the spinal cord 128 pass through the spinal canal 108 and foramina 111 to reach their respective destinations within the body.
The natural aging process can cause a deterioration of the intervertebral disks, and therefore, their intrinsic support strength and stability is diminished. Sudden movements may cause a disk to rupture or herniate. A herniation of the disk is primarily a problem when the nucleus pulposus protrudes or ruptures into the spinal canal 108 placing pressure on nerves which in turn causes spasms, tingling, numbness, and/or pain in one or more parts of the body, depending on the nerves involved. Further deterioration of the disk can cause the damaged disk to lose height and as bone spurs develop on the vertebrae 100, result in a narrowing of the spinal canal 108 and foramen 111 (not shown clearly), and thereby causes pressure on the nerves emanating from the spinal cord 128.
Presently, there are several techniques, in addition to non-surgical treatments, for relieving the symptoms related to intervertebral disk deterioration. Surgical options include chemonucleolysis, laminectomy, diskectomy, microdiskectomy, and spinal fusion.
Chemonucleolysis is the injection of an enzyme, such as chymopapain, into the disk to dissolve the protruding nucleus pulposus. The enzyme is a protein-digesting enzyme and is used to dissolve the disk material. Since the enzyme is essentially a tissue-dissolving agent, it is indiscriminate in the protein-based matter it dissolves. Should the enzyme be injected into the wrong place, or if there is a breach in the disk capsule that would allow the solution to enter the spinal canal or to contact nerve tissue or the like, the resultant damage to nerve tissue could not be reversed. Even worse, about half of the patients who receive chemonucleolysis treatments experience increased back pain and muscle spasms immediately after the injection and more than half have incapacitating back pain for durations up to three months after such treatments.
A laminectomy is performed to decompress the spinal canal by open surgical techniques under general anesthesia. In this procedure, the lamina 110, (the bone that curves around and covers the spinal canal 108 as shown in FIG. 9), and any disk tissue causing pressure on a nerve or the spinal canal 108, are partially removed. This technique is highly invasive and traumatic to the body, and therefore requires an extended recovery time of about five weeks and a hospital stay of a few days. In addition to the trauma inflicted on the body from even a successful surgery, there are increased risks of future problems due to the removed portion of the lamina 110 which is no longer in place to support and protect the spinal canal 108 at the area where the surgery took place. Further, the vertebrae 100 may shift due to the lack of support in the structure. Thus, simply removing the disk and parts of the vertebral bone is a short-term, pain-relieving corrective action but not a long-term solution.
Diskectomy is a form of spinal surgery wherein part of an intervertebral disk is excised typically through open surgical techniques. Recently, less invasive techniques referred to as percutaneous diskectomy or microdiskectomy have been developed to reduce the surgical trauma to the patient. In microdiskectomy, a much smaller incision is made than in normal open surgeries. A small retractor, working channel or tube is inserted through the posterior muscles (not shown) to allow access to the damaged or herniated disk. Surgeons utilize special surgical instruments modified to work in such small openings such as curettes, osteotomes, reamers, probes, retractors, forceps, and the like to cut and remove part of the disk while monitoring their technique using a microscope, a fluoroscope (real-time X-ray monitoring), and/or an endoscope (a miniature TV camera with associated viewing monitor). While this technique is much less invasive than conventional open surgeries, due to their design the instruments presently available tend to extend the length of time of the surgery and may cause possible damage to areas other than the herniated disk.
A spinal fusion is a procedure that involves fusing together two or more vertebrae in the spine using bone grafts and sometimes using metal fixation with screws, plates or metal rods. The removal of a significant amount of disk material or numerous surgeries often increases the instability of the spine 120 thereby necessitating spinal fusion surgery. The fusion procedure is often used to correct kyphosis or scoliosis, in addition to those patients who require spine stabilization due to vertebral damage from ruptured disks, fractures, osteomyelitis, osteoarthritis or tumors, and the like. In a fusion procedure, a damaged disk may be completely removed. Parts of a bone from another part of the body, such as the pelvis, are harvested, and the bone parts or grafts are subsequently placed between the adjacent vertebrae 100 so that the adjacent vertebrae 100 grow together in a solid mass. In the fusion surgery, which is presently performed as an open surgical technique, the posterior lamina 110 and the centers of the vertebral bodies 106 may both be cut. The surgery often involves consequential damage to the associated posterior ligaments, muscles and joints in addition to the removal of part or all of the lamina 110.
In general, small pieces of bone are placed into the space between the vertebrae to be fused, but sometimes larger pieces of bone are used to provide immediate structural support. The source of the bone may be the patient, (autologous or autograft bone) or a bone bank harvested from other individuals, i.e. allograft bone. While autologous bone is generally considered better for promoting fusion between the vertebrae, it also necessitates extra surgery to remove bone from the patient's body. As with any surgery, risks can include bleeding, infection, adverse reactions to drugs, and difficulty under anesthesia. Additionally, the site of the bone graft harvest may cause pain in addition to the pain the patient is already suffering due to the difficulties associated with the vertebrae 100 or disk. Due to the nature of the conventional spinal fusion surgery, typically an open surgery wherein muscles and ligaments are cut and bone is chiseled away to allow access to the intervertebral space, recovery following fusion surgery is generally longer than any other type of spinal surgery. Patients typically stay in the hospital for three or four days or more and may require significantly greater time to return to normal activities since the surgeon normally requires evidence of bone healing. The recovery time for a normal spinal fusion surgery is significant due not only to the fact that normal movement cannot be allowed until detectable bone growth has occurred between the bone grafts and the adjacent vertebrae 100, but the associated ligaments, muscles and the location where the bone grafts were harvested must also recover. Oftentimes portions of the spine 120 must be immobilized during the recovery period causing added discomfort and inconvenience to the patient.
The concept of using a cage device for spinal fusion is not new. Several fusion cages are disclosed in U.S. Pat. Nos. 4,961,740, 5,702,449, 5,984,967, and 6,039,762, the subject matter of which is incorporated herein by reference.
One prior art fusion cage device, disclosed in U.S. Pat. No. 4,961,740 of Ray et al. (hereinafter “Ray”), is a large cylindrically shaped fusion cage that has a deep helical thread around the outer surface. In order to install the fusion cage of Ray, laminectomies must be performed on each side of the overlying lamina in order to provide access for the large cylindrically shaped fusion cage and if the disk space has narrowed as a result of degeneration, a scissors jack-type spreader or hydraulically inflated bladder is inserted on each side and opened to allow access to the disk space. A pilot cutter and pilot rod are used to cut female bone threads through the opposing vertebral endplates prior to threading the fusion basket into the now threaded interdiskal bore. Obviously the surgery is lengthy, highly intrusive and traumatic, and as noted in the Ray specification takes several weeks for recovery.
Other prior art devices, disclosed in U.S. Pat. Nos. 5,702,449 and 6,039,762 of McKay (hereinafter, “McKay”), are cylindrically shaped spinal implants with perforations or apertures located through the outside walls. While the implants of McKay provide for a nonmetal, bone graft substitute, they still require open surgical techniques for implantation due to their size and geometric shape.
Further, the concept of using an implant device for spinal support and stability is not new. Implants were used by Dr. Fernstrom in the 1960's including stainless steel spherical ball bearings (see “Spine Arthroplasty,” Spine Industry Analysis Series, Viscogliosi Bros., LLC, November 2001.).
What is needed, but not provided in the prior art, is a stand alone vertebral defect device that can be inserted into the intervertebral space with minor open surgery in a procedure utilizing minimally invasive techniques. Further, there is a need for such a vertebral defect device which can be used either to assist with fusion or can be used to maintain support and stability while preserving motion of the involved spine segment.